H5N1 Bird Flu: What You Need to Know - Yale Medicine

[Originally published: May 16, 2024; Updated: May 23, 2024.]

Avian influenza A (H5N1), or bird flu, has killed millions of wild birds and caused sporadic outbreaks among poultry. Now, there is an ongoing multistate outbreak among cows in the United States. While bird flu is rare in humans, an infection in a dairy worker in Texas this past spring marked the first report in the U.S. of a cow-to-human H5N1 infection. In late May, a second dairy worker, this time in Michigan, tested positive, making it the second case linked to the outbreak in cows.

Meanwhile, in the wake of the COVID-19 pandemic, the thought of another virus with the potential to spread among humans is raising concern.

The good news is that there have been no reports of person-to-person bird flu transmission, and H5N1 is not considered a major public health threat in the U.S. at this time. The Centers for Disease Control and Prevention (CDC) has categorized the risk to the general public as "low," but continues to monitor the situation carefully.

"In the short term, there is very little threat," says Yale Medicine infectious diseases specialist Scott Roberts, MD. "In the long term, in the coming years or decades, however, I'm much more concerned." He gives two reasons: One is that there has been a mortality (or death) rate of about 50% in the almost 900 people around the world who have been infected with bird flu between 2003 and 2024.

However, 50% may be an overestimate, Dr. Roberts says, adding that there may be cases where people have no symptoms, are only mildly symptomatic, or haven't sought care for their symptoms. He also noted that if the virus did spread in humans, the percentage might be significantly lower if preventive approaches, including a vaccine, and treatments were made widely available.

Another reason for concern is that bird flu is now being detected in new animal species. In addition to outbreaks in cows—a relatively new development for the bird flu virus—there have been sporadic infections in some wild mammals. "It's natural to wonder if it's only a matter of time before this virus is able to spread among humans," Dr. Roberts says.

Below, Dr. Roberts answers eight common questions people have about bird flu.

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